1. Field of the Invention
The present invention relates generally to a wireless charging technology, and more particularly, to a received power conversion device for a resonant wireless charging system.
2. Description of the Related Art
Recent times have seen a growth in the development and implementation of wireless charging and non-contact charging technologies.
With the wireless charging technology, for example, wireless power transmission/reception can allow a battery to be automatically charged merely by being placed on a charging pad without connecting a separate charging connector to a cellular phone. Wireless electric toothbrushes and wireless electric shavers are well-known applications of the wireless charging technology. A waterproof function of the wireless charging technology improves portability and wireless charging of an electronic product, as the need for a wired charger is obviated. Moreover, wireless charging technology will likely be substantially applied to electric vehicles.
The wireless charging technology may be roughly divided into an electromagnetic induction type using a coil, a resonant using resonance, and a Radio Frequency (RF)/micro wave radiation type for transforming electrical energy into a microwave for delivery.
Power transmission using electromagnetic induction transmits power between a primary coil and a secondary coil. When a magnet is moved in a coil, induced current is generated, and is used by a transmission terminal to generate an electromagnetic field. In a reception end, current is induced according to a change in the electromagnetic field, thus producing energy. Such a phenomenon is referred to as a magnetic induction phenomenon and a power transmission method using this phenomenon has superior energy transmission efficiency.
As to the resonant, Soljacic, a professor at the Massachusetts Institute of Technology (MIT), disclosed as the coupled mode theory, a system in which by using a resonant power transmission principle, electricity is wirelessly delivered in spite of a distance of several meters from a charging device. The wireless charging system of the MIT team resonates an electromagnetic wave containing electrical energy. The resonated electrical energy is directly delivered only when there is a device having a resonance frequency, and the non-used portion of the resonated electrical energy is absorbed again into an electromagnetic field, instead of being spread through the air, such that unlike other electromagnetic waves, the resonated electrical energy does not appear to have an influence upon a peripheral machine or the human body.
A wireless power receiver of a conventional resonant has to consider the use of a rectifying circuit for converting a received Alternating Current (AC) waveform into a Direct Current (DC) waveform, a DC-DC converting circuit for adjusting rectified DC-waveform power to a preset voltage value of an output end, and a plurality of large-capacity passive elements. Thus, significant restrictions may exist in their mounting sizes.
Such restrictions give rise to difficulties in applying a wireless charging system to such size-sensitive devices as a portable terminal.
Consequently, there is a need in the art to reduce the sizes of wireless charging related devices while providing them with high power and efficiency.